Manny Pacquiao is used to the frenzy. Tens of thousands of fans bob and throng feverishly in front of the stage in the heavy, sticky heat of a tropical night. Young and old, rural and urban, devout and secular: all are eager for a glimpse of the man who is undeniably the Philippines' most famous sporting hero.

For a man who is a boxing phenomenon, it is a familiar scene. Pacquiao is used to punishing opponents in front of crowds like this. Only on this occasion, he is turned out not in his trademark red flame-emblazoned white shorts and robe but in jeans and an orange shirt.

A natural entertainer, he cradles a guitar and shows off another string to his bow: a singsong-like baritone that belts out a campaign tune.

"I would not be where I am today without you, and now I want to help the Philippines," he declares, warming to his theme. "What is important is my relationship to God and to the Filipino people."

Pacquiao's rise from extreme poverty to sporting superstardom is a narrative that resonates with many Filipinos. But as the campaign for the crucial 10 May general elections intensifies here, the man considered the best pound-for-pound fighter the world has ever seen, with 51 wins out of 56 bouts in a 17-year career, is facing a far greater challenge than just another welterweight slugger in the ring.

In running for Congress in a rural province of Mindanao, Pacquiao joins a rare group of athletes who have sought to make the leap from sportsman to statesman.

"Boxing is about honour," he tells the Guardian in an interview during some rare downtime in a pool bar that he owns in General Santos City. "Now I want to be known as a good public servant. I want to be known as a generous person."

Politically, it is a seductive message. Forty per cent of Filipinos live on less than $2 (£1.30) a day. Pacquiao has already been drawing on a personal fortune estimated at upwards of $40m to support projects in his province such as one that provides drinking water for impoverished areas.

Sometimes he opts for instant charity: guards at his mansion say he rarely leaves home without giving cash to the crowds of destitute people who gather there each day. His electoral pitch is that he would lobby for the most basic needs of the 600,000 people in his district: livelihood programmes, free education, healthcare and medical assistance.

"That's the major problem right now," he says after shooting a few frames of pool with some friends. "Do they need money? No. They need livelihood, to feed their family. They will not ask the government to help them if they have work."

The fever surrounding "Pacman", as he is known, is heady. But some sceptics note that sports stars do not always fare well in politics.

The economist Winnie Monsod, a professor at the University of the Philippines, says she does not doubt his sincerity. But she warns: "I am not ready to translate that sincerity into actual deeds, because the other politicians he associates with do not exactly have the highest reputation for integrity."

Pacquiao has aligned himself with the presidential candidate Manny Villar, who is taking on a colourful slate of candidates. Among these are Benigno Aquino, the son of the former president Corazon Aquino, and the disgraced ex-president Joseph Estrada. Imelda Marcos, the widow of the former dictator, is also running for Congress.

Pacquiao's failed attempts at an acting and singing career may also indicate people's lack of readiness to accept him in a new role. "They love him as a boxer but may not be ready to take him in any other capacity," Monsod says, adding that he failed to get elected three years ago for that very reason.

Pacquiao's politics are informed by early years that millions here can relate to. The eldest of six children living with a single mother, he became the provider at a young age, spending his days finding food, water and shelter. He has said: "We were so poor I tried to sleep outside in a cardboard box when I was 10 years old. And some days, I didn't eat.

"I feel what the people feel right now because I have been there. We need a leader who has experienced this and who will never forget it."

For a merciless pugilist, Pacquiao is surprisingly eloquent, communicating with a simplicity as powerful as his jabs. He prays at least three times a day, and has a priest come to the dressing room for prayer before each fight.

His bodyguard, Ernesto Madidis, says Pacquiao's faith is a core value. "He really doesn't change. He never turned his back on where he comes from. He still plays with the friends he had when he would sell doughnuts at 4am, and still knows the name of everyone in the area he grew up in."

Other supporters, such as Zed Protactio, are taken by his generosity: "He is not thinking of himself but of the people," Protactio says. "Most politicians are not like this. Even before he entered politics, he had a track record of helping people. He is not materialistic. He has enough, so gives the rest."

The majority of Filipino voters are tired of a deeply corrupt political system in which candidates make promises during their campaigns only to forget them later. Pacquiao's team says the boxer intends to lead by example. But even if he wins – and his team admits he has a fight on his hands, against a candidate from a dominant local family – he may find it hard to punch his weight.

As a legislator in a parliament renowned for balking at passing bills to help disenfranchised and marginalised sectors of society, Pacquiao's influence may be limited. He refuses to be drawn on whether he sees Congress as just a first step towards higher political office.

Monsod said: "He needs to be able to sell his ideas. What he is saying about not being corrupt is not enough to make him an effective politician."

Pacquiao's ability to transform ideas into action will also depend on how well the Nacionalista party, led by Villar, does at the polls, Monsod said – and on whether, if his political career does take off, he acts as a member of the club that holds power.